1. Field of the Invention
The present invention relates generally to the field of solid-state image sensing devices, and more particularly, the present invention relates to an improved solid-state image sensing device and method of processing image information.
2. Description of the Related Art
Some solid-state image sensing devices, such as, for example CCD area sensors, have a structure that includes a drain section 103 for discharging signal charge and a sweep-out electrode 104 as shown in FIG. 13. These structures are provided on the side opposite an image section 101 of a horizontal transfer register 102. Application of a sweep out clock .phi.HOG to the sweep-out electrode 104 for a given period, sweeps out the signal charges in the horizontal transfer register 102 to the drain section 103.
On the other hand, some CCD area sensors generally have a horizontal transfer register 102 with a wide channel width for increasing the capacity for involved charges because the pitch in the horizontal direction of the horizontal transfer register 102 is inevitably determined by the number of pixels and the optical system. In particular, the charge capacity of the horizontal transfer register 102 is proportional to the area per 1 bit under the condition of constant amplitude of the transfer clock, and therefore the charge capacity can be increased by increasing the length and width for one bit. However, the length is limited by the number of pixels of the image section 101 and only the channel width can therefore be increased.
In a CCD area sensor provided with a horizontal transfer register 102 with a wide channel width, if the structure for selectively sweeping out the signal charge in the horizontal transfer register 102 as described herein above is applied, it has been difficult to completely sweep out the signal charge within a predetermined time because the transfer electric field from the horizontal transfer register 102 to the drain section 103 is weak, particularly the transfer electric field at the middle portion in the width of the channel is weak when the signal charge in the horizontal transfer register 102 is intended to be swept out to the drain section 103 through the sweep-out electrode 104. In order to sweep out the signal charge in the horizontal transfer register 102, it takes a long time for sweeping out charges, and high speed sweeping out has been difficult to achieve.
This is true not only for a CCD area sensor having one horizontal transfer register 102 but also for a CCD area sensor having a structure which includes two or more horizontal transfer registers such as registers 102a and 102b shown in FIG. 14. This structure is provided with a transfer electrode 105 between both registers 102a and 102b in order to independently horizontally transfer and output the signal charge of two vertical lines for one horizontal period. A drain section 103 and sweep-out electrode 104 are provided adjacent to the outside horizontal transfer register 102b in order to selectively sweep out the signal charge in the horizontal transfer registers 102a and 102b.
As described herein above, the CCD area sensor having two horizontal transfer registers 102a and 102b can independently read the signal charge of all pixels of the image section (so-called all pixel reading) by independently reading signal charge of two vertical lines for one horizontal period. Therefore, the vertical resolution is improved in comparison with a device that reads signal charges for two vertical lines which are mixed. For a CCD area sensor of this sort, it is inevitable that the channel width of each is widened in order to increase the charge capacity of the horizontal transfer registers 102a and 102b. Thus the residual transfer of signal charge due to the decrease of the transfer electric field is a problem, as is true for a CCD area sensor having one horizontal transfer register 102.
This invention is accomplished in view of the above-mentioned problem. One object of the present invention to provide a solid-state image sensing device capable of completely sweeping out the signal charge in a horizontal transfer register and for sweeping out the signal charge to a drain section. Another object of the present invention is to provide a device which is capable of high speed sweeping out operation and a method for driving thereof. Yet another object of the present invention is to provide a device and method of processing CCD video information wherein only a portion of the complete image is initially processed at a higher speed and the remaining portion of the image is stored and later processed or processed initially at a slower speed. Other objects and advantages of the present invention will be apparent from the following summary and detailed description of the invention when viewed in light of the drawings.